Building 3D GIS data models using open source software

Abstract

Today, many GIS applications would require data sets containing full 3D data; application fields like urban and town planning, civil protection, cadastres and environmental studies could use full 3D data, both to carry out spatial analyses and inquiries as well as for only visualization. Data model can be accessed by desktop application as well as from Internet. This second option is becoming today the most requested. But in order to share 3D data model through Internet it is necessary to configure a suitable system. A 3D model can be shared on Internet in different ways. It is possible to incorporate a model inside an executable or 3D PDF file or build something like a multimedia application (i.e. flash based). However a better option is to put a model inside a geospatial database and build suitable web services to access it using Internet browsers. This second option can be performed using different solutions for web servers, development platforms and programming languages. Fundamental for this option is the construction of the model that should be structured, according a conceptual model to be replicable and interoperable. Hence, the model should be stored in a geospatial database in order to be accessed by an application running under a web server, so allowing access to the model. All this is the object of the research—Management and use of distributed 3D data by open source WebGIS software—that is part of the Italian PRIN 2007 research project: Interoperability and cooperative management of geographic, dynamic, multi-dimensional and distributed data with Free and Open Source GIS (Principal investigator Paolo Zatelli), aimed to build urban and suburban 3D models with CAD software or solid modellers, share them with a 3D Web Feature Service Open Geospatial Consortium web feature service like, and them using Internet browsers all done using only free and open source software. The research work, here illustrated, which was funded by previous research project, deals with the construction of a suitable model and the storage of the model inside a geospatial database. The work is based on the use of free and open source software; Blender and PostgreSQL with PostGIS have been used, respectively, to draw objects of the model and save their data with the help of some Python scripts; the server side part of the system has been realized using Tomcat with servlets and applets all written in Java. Buildings have been modelled according to GIANT3D model (Geographical Interoperable Advanced Numerical Topological 3-Dimensional Model) previously developed in the research "PRIN 2004", regarding "Evolved structure of numerical cartography for GIS and WebGIS". Python scripts, activated by Blender, allow saving data into a spatial database implemented through PostgreSQL and PostGIS that could be a remote database somewhere on the net; all geometrical and topological information, implemented in the 3D model, is so transferred in PostGIS. This information can be retrieved by Blender using other Python scripts, so Blender fully interacts with 3D data allocated in PostGIS. These data can be also accessed by many other clients, both directly using a database client and using other protocols (like HTTP on Internet). The second part of the research deals with the creation of a 3D Web Feature Service and an applet for internet browsers, in order to allow clients to visualize, explore and inquiry 3D model, retrieving data from database.

Appendix A

Parts of script that reads geographical information from a table (three-dimensional points or lines) on PostGIS database and draws points or a polyline

Parts of script that connects to database and writes information using triangular face model

Full versions of scripts are available at http://www.dirap.unipa.it/python_scripts or also at http://gislab.geomatica.unipa.it/index.php/attivita-di-ricerca/2-uncategorised/8.